(32) “Isaac his father said to him, “Who are you?” (33) And he said, “I am your son, your first-born, Esav.” And Isaac trembled a great trembling, and said, “Who – where – is he, the one who caught game and brought it to me, and I ate of all when you had not yet come, and I blessed him? He shall also be blessed!” (34) When Esav heard his father’s words, he cried out an exceedingly great and bitter cry, and said to his father, “Bless me too, Father!” (35) But he said, “Your brother came with cleverness and took your blessing.” (36) He said, “Was his name called Jacob, and he outwitted me these two times? – He took away my birthright and see, now he took away my blessing!”
Rashi comments: Why did Isaac tremble? He said, “Perhaps I have sinned, that I have blessed the younger ahead of the elder, and I deviated from the order of lineage?” Esav began to cry out, “He outwitted me these two times!” His father said to him, “What other thing did he do to you?” Esav said to him, “He took my birthright as firstborn.” Isaac said, “Over this was I distressed and trembling, lest I crossed the line of the law. Now I see that I blessed the firstborn. “He shall also be blessed.”
Rashi explains that Yitzchak exclaimed “He shall also be blessed” when he realized that Esav had sold the first-born right to Yakov. Yakov was the deserved recipient of the blessing. No mistake had been made.
The order, however, is problematic. As can be seen above, “He shall also be blessed” (verse 33) was exclaimed well before Esav admits that he sold the first-born right to Yakov (verse 36).